Non-degradative drying of sodium triphosphate hexahydrate



Unite States atent 3,063,801 Patented Nov. 13, 1962 ice No Drawing. Filed July 25, 1958, Ser. No. 750,860 9 Claims. (Cl. 23107) The present invention relates to methods for the dehydration or drying of sodium triphosphate hexahydrate, as well as mixtures containing sodium triphosphate hexahydrate, including aqueous slurries containing sodium triphosphate hexahydrate alone or in admixture with other components It is an object of the invention to manufacture sodium triphosphate in anhydrous or hydrated form as well as commercial detergent compositions containing sodium triphosphate without degrading this compound. It is also an object of the invention to prepare an anhydrous form of sodium triphosphate as a pure compound, or as compositions having controlled proportions of the said anhydrous form in combination with the hexahydrate. Further objects of the invention will appear hereinafter.

It has been recognized in the detergent art that sodium triphosphates are desirable components of detergent compositions. It has been found, however, that the sodium triphosphate is readily degraded or decomposed in ordinary drying operations with loss of its water of crystallization and with resultant hydrolysis to other phosphate salts. The hydrolysis of the hexahydrate to acid salts of ortho phosphoric acid and pyrophosphoric acid has been stated in the prior art to occur when the water of hydration is removed at temperatures below 250 C.

The expedients which have been tried to avoid degradation of sodium triphosphate include control of the degree of hydration of the original anhydrous phosphate by varying the time of contact with water, and also controlling the time of heating in the spray drying operation. The present method makes it unnecessary to employ such expedients. Earlier investigators who have tried to dehyrate sodium triphosphate hexahydrate have suggested that the hydrolysis which occurs upon the evaporation of water from the hydrate can best be prevented by the rapid removal of Water from a shallow bed of the material. However, this solution has not been found to be practical. The manufacture of commercial detergent mixtures such as those based upon synthetic organic detergent components together with sodium triphosphate hexahydrate has been hindered by difficulties due to degradation of the said triphosphate. In particular it has been found that the temperatures required in spray drying of the detergent slurries bring about considerable hydrolysis of the triphosphate resulting in the formation of other phosphates, such as acid salts of orthophosphoric acid and pyrophosphoric acid. It is a disadvantage of such degradation products that they are less alkaline than sodium triphosphate and have less dispersing and sequestering ability and hence are distinctly inferior to triphosphate as builders for synthetic detergents. They are thought also to contribute to such undesirable characteristics of the product as stickiness, dustiness, caking and balling.

The invention herein set forth is based upon a control of the degradation or reversion of sodium triphosphate, either in anhydrous or in hydrated form, to orthophosphates and pyrophosphates, which is otherwise found to occur when the Water of crystallization is removed from sodium triphosphate hexahydrate under normal drying conditions at any temperature below 250" C. Substantially pure form II, anhydrous sodium triphosphate, has been foundto be obtained if during the drying process a critical pressure of water vapor or steam is maintained surrounding the sodium triphosphate hexahydrate. This is a totally unexpected and novel result, since sodium triphosphate has been considered to be thermodynamically unstable in the presence of water. Consequently, the prior knowledge has predicted that increasing Water vapor pressure would delay the removal of water from the hydrate and so increase the tendency for the sodium triphosphate to degrade according to a reaction typically represented by:

The complete or partial dehydration of sodium triphosphate hexahydrate, so as to produce anhydrous sodium triphosphate or a mixture of hydrated and anhydrous forms of the triphosphate in any desired proportions with a minimum of orthophosphates and pyrophosphates, may be obtained by means of the present process. In this method as applied to a spray drying process, an aqueous slurry containing the sodium triphosphate hexahydrate is dispersed in a drying tower and falls in droplet form through the tower in countercurrent flow to an ascending heated gas stream.

The present method is of general utility and may be practiced in various ways in order to contact sodium triphosphate hexahydrate, alone or in admixture with other components, with a gas containing water vapor. Spray drying constitutes one embodiment of the invention, other embodiments include the use of calciners, tubular reactors, fluidized beds and other solid-gas contacting means.

The essential element of the invention in the contacting of sodium triphosphate hexahydrate by any of the above methods to obtain a product of the desired water content without degradation, is that the inlet temperature of the drying gas be within the range of from 110 C. to 900 C. It is essential that the water vapor content of the drying gas must be suflicient to maintain a partial pressure of 190 mm. Hg. For example, at one atmosphere (760 mm.) the water vapor content is 25% by volume. It is likewise essential that the water vapor pressure shall not be greater than corresponds to a relative humidity of 40% at the inlet temperature of the drying gas. A preferred range of operation is to employ a gas inlet temperature of 300 C. to 330 C., and a preferred range of water vapor content of the drying gas is that corresponding to a partial pressure of water vapor of about 300 to 600 mm. Hg. For example, at 760 mm. total pressure, the steam present amounts to 40% to by volume relative to the total volume of gas.

The heated gases employed in the persent invention may be derived by direct or indirect heating methods. As an example of the direct heating, natural gas or other fuel gases are burnedwith air or with oxygen-supplemented air in order to yield a hot flue gas. The general temperature range for this purpose is from C. to 900 C., while a preferred range of gas inlet temperatures measured at the point wherein the hot gas stream first enters the drying system is from 300 C. to 330 C. Indirect heating of the contacting gases may also be practiced such as by 'means of a steam heat exchanger, through which air is passed before being admitted to the drying chamber. In this way it is also possible to make use of extremely dry air or other heating gases, since the gas stream may be passed through a conventional drier such as an alumina drier before being heated.

In the event that the product contains some sodium triphosphate hexahydrate in the presence of anhydrous sodium triphosphate, the product is cooled rapidly to a temperature of less than 60 C. in a dry atmosphere, such as by allowing the product to fall into a cooled con veyor through a small counter-current flow of ldry air. Other cooling devices common in the art may similarly be employed. The treatment time for the present invention is not critical but may be varied in the range of from 3 seconds to 60 minutes. It is obvious that the use of higher temperatures permits the use of shorter reaction times.

It has been found that the use of steam in accordance with the above limitations directs any decomposition of sodium triphosphate hexahydrate essentially in accordance with the equation below.

In this way it is possible to control not only the degradation, but also the relative proportion of hexahydrate in combination with the anhydrous compound. Thus, it is possible to prepare a detergent composition in which the phosphate content is present to a large degree as sodium triphosphate hexahydrate.

In the manufacture of detergent compositions in accordance with the present invention, the various non-soap organic and inorganic compounds may be present in the starting mixture which is to be spray dried. Typical of such detergent components are the organic sulfonates or sulfates or mixtures thereof, which are provided as alkali metal salts. Examples of such alkylated aromatic hydrocarbon sulfonic acid compounds include the dodecyl benzene sulfonic acid compound generally employed as the sodium salts.

Other syntheticorganic detergent components contemplated in the present invention include a wide variety of detergent components which may be present in the sodium triphosphate mixture which is to be subjected to a drying operation in accordance with the present invention. Such detergent components include the various types of soaps and also the synthetic, organic, detergent components including the anionic and non-ionic types. Examples of the anionic and non-ionic detergent components employed in the present invention include the sulfate and sulfonate type compounds as typical anionic detergents. Representative compounds of the non-ionic type are the ethers and esters (including sulfur-containing derivatives and analogles) of polyalkylene glycols and polyglycerols. Mixtures of the above detergent components may also be employed. 7

The aliphatic sulfated or sulfonated detergents which are employed may have from 8 to 26 carbon atoms.

Such detergents include the aliphatic, acyl-containing compounds having an 'acyl radical of about 8 to 26 carbon atoms such as the aliphatic carboxylic ester detergents. Examples of aliphatic anionic detergents are the sulfuric acid esters of polyhydric alcohols incompletely esterified with higher fatty acids, for example, cocoanut oil monoglyceride mono-sulfate, tallow diglyceride monosulfate, the long-chain pure or mixed higher primary and secondary alkyl sulfates, such as lauryl sulfate, cetyl sulfate, and higher fatty acid alcohol sulfates derived from reduced cocoanut oil fatty acids. Other compounds which may be used in the present combination include the hydroxy sulfonated higher fatty esters, for example, the

' higher fatty acid esters of 2,-3-dihydroxy propane sulfonic acid, and the higher fatty esters of low molecular weight alkylol sulfonic acids, such as the oleic ester of isethionic acid. The invention also contemplates the use of higher fatty ethanolarnide sulfates, the higher fatty acid amides of amino alkyl sulfonic acids, for example lauric amide of taurine, etc. The salts of the various compounds employed in the present invention are preferably the sodium,

ammonium or potassium salts.

One of the preferred types of detergent components is a sodium or ammonium sulfonate of an alkyl-substituted aromatic hydrocarbon selected from the group consisting of benzene, toluene and xylene, wherein the alkyl group has from 9 to 18 carbon atoms. The alkylaryl hydrocarbon is sulfonated and is then neutralized with a sodium, potassium or ammonium alkaline compound to obtain the corresponding sodium, potassium, or ammonium salt. In the preparation of the alkylaryl sulfonate, the alkyl group is preferably of about 10 to 12 carbon atoms average length, such as may be obtained from olefins or from kerosene. The kerosene may be chlorinated and the aromatic compound alkylated therewith in known manner. Another available composition of this type is produced by alkylating the aromatic hydrocarbon with an olefin hydrocarbon averaging 9 to 18 carbon atoms in the molecule, and thereafter sulfonating and neutralizing the product. Compounds of the sulfonate type are described in US. Patents 2,232,117 and 2,232,148 to Kyrides. A preferred compound of this type is sodium dodecyl benzene sulfonate, also known as sodium tetrapropyl benzene sulfonate when derived from tetrapropylene and benzene.

Other compounds of the above category of anionic detergents having utility in the present invention include the sulfated esters such as the sulfated esters of succinic acid and of sulfophthalic acid. Examples of such compounds which may be employed in the present detergent compositions are the sodium salt of dioctyl sulfosuccinate, sodium hexyl-4-sulfophthalate and octadecyl sulfophthalate. The present invention may also employ sulfonates of an acid which is esterified with a monohydric alcohol. A salt of this type of compound is sodium tridecyl ,B-sulfopropionate.

Another group of useful detergent compounds are the sulfated and sulfonated anionic detergents based on alkyl phenols or long chain, fatty alcohols and tall oil condensed with ethylene oxide or propylene oxide. Examples of such compounds are the sodium, ammonium or amine (e.g., triethanolamine) salts of nonyl phenol condensed with ten moles of ethylene oxide and then sulfated, while another compound is tridecanol condensed with ten moles of ethylene oxide and then sulfated.

The anionic detergents are generally employed in the form of water-soluble salts, such as the alkali metal salts described above. However, the alkaline earth metal, ammonium, amine, and alkylolamine salts are likewise of utility in the present invention. While the sodium, potassium, ammonium and alkylolamine (e.g., monodiand triethanolamine) salts are ordinarily preferred, other salts such as the lithium and magnesium salts may be used if desired. For certain purposes, as in the attainment of the maximum solubility, the ammonium and alkylolamine salts are preferred.

The non-ionic compounds which are employed in the present invention include the polyoxyethylene ethers of aliphatic alcohols having straight and branched chain configurations. Long chain derivatives of polyhydroxy compounds such as the ethers of polyalkylene glycols may also be employed in the present detergent compositions. Other compounds include the polyoxyethylene ethers of alkyl aromatic hydroxy compounds, for example, the'alkylated polyoxyethylene phenols.

A typical compound of this group is the ethylene oxide condensation product of a highly branched monohydric primary alcohol such as tridecanol, having the molecular configuration of an alcohol produced by the 0x0 process from an olefin such as triisobutylene or tetrapropylene, with from 1 to 20 moles of ethylene oxide per mole of alcohol. A preferred range is from 5 to 10 moles of ethylene oxide. The present invention includes the use of a mixture of isomeric monohydric primary tridecyl alcohols, said alcohols being derived from the 0x0 process carried out with a material of the class consisting of polybutylenes and polypropylenes.

Another detergent component of the polyoxyethylene condensate type is the product obtained by the condensation of tall oil with ethylene oxide. The condensation of tall oil with ethylene oxide may be conducted with from 1 to 20 moles of ethylene oxide per mole of the tall oil, a preferred range being from 5 to 15 moles of ethylene oxide. Another condensation product of this type which is useful in the present invention is the product resulting from the condensation of tertiary octyl or nonyl phenol with from 5 to 20 moles of ethylene oxide per mole of the said phenol.

Polyoxyethylene compounds containing sulfur are also of utility. A compound of this type which may be employed in the present invention is the condensation product of a tertiary mercaptan having from 6 to 20 carbon atoms, condensed with from 5 to 20 moles of ethylene oxide per mole of mercaptan.

The above described polyalkylene condensation products may be prepared from propylene oxide as well as with ethylene oxide. Adrnixtures of these two condensing agents may also be employed.

Another synthetic, organic detergent component which may be employed in the present invention is a compound selected from the group of alkanolamides of fatty acids, preferably having from 10 to carbon atoms. A preferred compound of this type is lauric diethanolamide derived from diethanolamine and crude lauric acid. Other acids and mixtures thereof may similarly be employed for this purpose. For example, an alkanolamide may be prepared from the fatty acids derived from tall oil during the purification and fractionation thereof. The alkanolamine which is employed to form the preferred alkylolamides may be monoor diethanolamine, monoor diisopropanolamine, or monoor di-n-propanolamine. Preferred amines are diethanolamine and monoethanolamine.

Other sources of fatty acids which may be used in the preparation of the alkylolamides are the naturally occurring fatty acids, such as those derived from cocoanut oil. The said cocoanut oil fatty acids are within the present preferred group of fatty acids having from 10 to 20 carbon atoms in the acid radical.

In addition to the active detergent components described above, the present detergent compositions may include other builders and additives, such as sodium silicates, sodium sulfate, fluorescent dyes, perfume and carboxy methyl cellulose.

The following examples illustrate specific embodiments of the present invention:

Example 1 A sample of pure sodium triphosphate hexahydrate was dried to the anhydrous form by passing steam at 150 C. through a fluidized bed of the hydrate for 24 minutes. These conditions corresponded to about 20% relative humidity. The product after treatment was identified as anhydrous sodium triphosphate by X-ray diffraction. No tetrasodium pyrophosphate was detected, indicating that substantially no degradation took place. In a control experiment in which dry air was used to contact the sodium triphosphate hexahydrate, the product contained 20% tetrasodium pyrophosphate and only 40% of the desired anhydrous sodium triphosphate, while the remainder was an amorphous mixture of orthophosphates and pyrophosphates.

Example 2 A sample of pure sodium triphosphate hexahydrate was dried at 140 C. in an atmosphere consisting solely of water vapor maintained at 200 mm. Hg pressure and a relative humidity of 7.5%. Drying was complete in 40 minutes. The only crystalline product detected by X-ray diffraction was Form II anhydrous sodium triphosphate. Degradation products were present only in small proportion.

In another experiment in which the water vapor pressure was controlled at 135 mm. Hg in the drying of sodium triphosphate hexahydrate at 140 C., the reaction required 55 minutes for completion. X-ray diffraction showed the product in this case to contain 34% tetrasodium pyrophosphate, indicative of major degradation,

and only 13% of Form II sodium triphosphate, anhydrous.

Example 3 In carrying out a countercurrent spray drying operation, a slurry containing 60% by Weight of sodium triphosphate hexahydrate was fed to a spray drying tower. The drying gases obtained by the direct combustion of natural gas with air were charged to the spray drying tower, together with sufficient saturated steam at 100 pounds pressure to provide a water content at the inlet corresponding to 450 mm. partial pressure, or about 60% by volume of the total. The inlet temperature was maintained at 315 C. A dry, free-flowing product was removed from the bottom of the tower which was found to contain 11% moisture. The product was analyzed as 96% triphosphate with 45% in the form of the hexahydrate.

In a control experiment in which no water vapor was injected, the product was hygroscopic, becoming gummy and Sticky. It contained only 50% triphosphate with 47% in the form of the hexahydrate. Thus, nearly all hexahydrate which had dehydrated had been degraded.

Example 4 The method of Example 3 was carried out utilizing a detergent slurry containing the following components (wt. percent):

Percent Sodium dodecyl benzene sulfonate 13 Sodium triphosphate hexahydrate 20 Sodium sulfate 8 Soda ash--- 2 Sodium silicate (Na O/SiO ratio 1:2.8) 3 Water 54 The method of Example 3 was carried out utilizing a detergent slurry containing the following components (wt. percent):

Percent Condensation product of tall oil condensed with an average of 7.2 ethenoxy groups by reaction with ethylene oxide 8 Sodium triphosphate hexahydrate 20 Sodium silicate (Na O/SiO ratio 122.8) 5 Sodium sulfate 5 Soda ash 10 Water 52 The slurry dried readily with a water vapor content of 50% in the entering gas in the countercurrent drying operation to yield a satisfactory free-flowing detergent mixture. Recovery of the sodium triphosphate was However, in a control experiment conducted without the presence of water vapor the sodium triphosphate recovery was only 45 and the product was excessively gummy.

What is claimed is:

1. Method for the production of anhydrous sodium triphosphate from sodium triphosphate hexahydrate without degradation which comprises contacting a mixture of sodium triphosphate hexahydrate and water with a stream of heated gas at a temperature of from C. to 900 C. containing water vapor at a partial pressure of at least mm. Hg, but with a relative humidity less than 40% and thereafter collecting the said anhydrous sodium triphosphate product.

2. Method for the production of anhydrous sodium triphosphate from sodium triphosphate hexahydrate without degradation which comprises contacting a mixture of sodium triphosphate hexahydrate and water with a stream of heated gas at a temperature of from 300 C. to 330 'C. containing water vapor at a partial pressure of from 300 to 600 mm. Hg. and thereafter collecting the said i anhydrous sodium triphosphate product.

3. Method for the production of anhydrous sodium triphosphate from sodium triphosphate hexahydrate without degradation which comprises contacting a mixture of sodium triphosphate hexahydrate and Water with a stream of heated gas containing water vapor at a partial pressure of from 300 to 600 mm. Hg, and with the said heated gas having a temperature of from 110 C. to 900 C. and thereafter collecting the said anhydrous sodium triphosphate product.

4. Method for the production of sodium triphosphate in anhydrous form from a mixture of sodium triphosphate hexahydrate with water without degradation which comprises spray drying in aqueous slurry containing sodium triphosphate hexahydrate countercurrent to a stream of heated gas at a temperature of from 110 C. to 900 C.

containing water vapor at a partial pressure of at least 190 mm. Hg, but with a relative humidity less than 40% and thereafter collecting the said anhydrous sodium triphosphate product.

5. Method for the production of sodium triphosphate in anhydrous form from a mixture of sodium triphosphate 'hexahydrate with water without degradation which comprises spray drying an aqueous slurry containing sodium triphosphate hexahydrate countercurrent to a stream of heated gas at a temperature of from 300' C. to 330 C. containing water vapor at a partial pressure of about 330 to 600 mm. Hg and thereafter collecting the said anhydrous sodium triphosphate product.

6. Method for the production of sodium triphosphate in anhydrous form from a mixture of sodium triphosphate hexahydrate with water Without degradation which comprises spray drying an aqueous slurry containing sodium triphosphate hexahydrate countercurrent to a stream of heated gas containing water vapor at a partial pressure of about 300 to 600 mm. Hg, and in which the heated gas is at a temperature of from C. to 900 C. and thereafter collecting the said anhydrous sodium triphosphate product.

7. Method for the production of mixtures of sodium triphosphate hexahydrate with anhydrous sodium triphosphate without degradation from an aqueous slurry comprising sodium triphosphate hexahydrate which comprises contacting the said aqueous slurry with a heated gas at a temperature of from 110 C. to 900 C. at a partial pressure of at least mm. Hg, but with a relative humidity less than 40%, and thereafter collecting the said mixture containing a substantial amount of anhydrous sodium triphosphate.

8. Method for the production of mixtures of sodium triphosphate hexahydrate with anhydrous sodium triphosphate without degradation from an aqueous slurry comprising sodium triphosphate hexahydrate which comprises contacting the said aqueous slurry with a heated gas at a temperature of from 300 C. to 330 C. at a partial pressure of from 300 to 600 mm. Hg, and thereafter collecting the said mixture containing a substantial amount of anhydrous sodium triphosphate.

9. Method for the production of mixtures of sodium triphosphate hexahydrate with anhydrous sodium triphosphate without degradation from an aqueous slurry comprising sodium triphosphate hexahydrate which comprises contacting the said aqueous slurry with a heated 'gas at a partial pressure of from 300 to 600 mm. Hg,

and with the said heated gas having a temperature of from 110 C. to 900 C., and thereafter collecting the said mixture containing a substantial amount of anhydrous sodium triphosphate.

References Cited in the file of this patent Industrial and Engineering Chemistry, Molecularly Dehydrated Sodium Phosphates, Hafiord, volume 46, No. 9, September 1954, pages 1938-1941.

P. Bonnemann-Bemia, Annales de Chimie, Translation of Contribution Phosphoric Acids, vol. 16, pages 395-425 (1941). 

1. METHOD FOR THE PRODUCTION OF ANHYDROUS SODIUM TRIPHOSPHATE FROM SODIUM TRIPHOSPHATE HEXAHYDRATE WITHOUT DEGRADATION WHICH COMPRISES CONTACTING A MIXTURE OF SODIUM TRIPHOSPHATE HEXAHYDRATE AND WATER WITH A STREAM OF HEATED GAS AT A TEMPERATURE OF FROM 110*C. TO 900*C. CONTAINING WATER VAPOR AT A PARTIAL PRESSURE OF AT LEAST 190 MM. HG, BUT A RELATIVE HUMIDITY LESS THAN 40% AND THEREAFTER COLLECTING THE SAID ANHYDROUS SODIUM TRIPHOSPHATE PRODUCT. 